System for maintaining substantially constant tension for rewind drives



March 28, 1961 c. I AwLER-wlLsoN 2,977,061

FOR MAINTAIN SYSTEM ING SUBSTANTIALLY CONSTANT TENSION FOR REWIND DRIVES Filed Jan. 20, 1958 KN ne wm Si@ l @N um NW. OU

INVENTOR.

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SYSTEM FOR MAINTAINNG SUBSTANTIALLY CONSTANT TENSIGN FOR REWI'ND DRIVES Clive Lawler-Wilson, Los Angeles, Calif., assigner to 'U.S. Electrical Motors, Inc., Los Angeles, Calif., a corporation of California Filed Jan. 20, 1958, Ser. No. 709,829-

11 Claims. (Cl. 242-75.51)

This invention lrelates to a system for controlling the speed of a rewind reel or drum upon which a strip or web is to be wound.

4it is often desirable to maintain a constant tension upon a metal or fabric strip as it is wound on a mandrel. For example, `an aluminum strip after it leaves the cold mill, may be tensioned as it is wound to produce a stretch. The control of tension is therefore important. It is also important, in o-rder to prevent marring of the finish, that this control be effected without physical contact of the strip with dancer rolls or the like commonly employed heretofore for such controls.

it is one of the objects of this invention to make it possible to maintain the tension of the web or strip within tolerable limits, and yet without the aid .of any tactile elements, such as dancer rolls.

In accomplishing these results, an electric motor is ernployed for driving the rewind roll. This motor is con nected to the roll through a transmission mechanism, the speed ratio of which can be varied in a continuous manner. As the roll increases in diameter, the speed must be continuously reduced in order to keep the tension at the desired value.

The torque required to be exerted by the motor is proportional to the product of the tension and the effective radius of the roll; and the power is proportional to the product of the torque and the speed. As the torque increases due to the increase in radius, the speed is proportionately decreased; therefore, ideally, the motor has a useful power output that should remain substantially constant throughout the range of the rewind operation.

It is one of the objects of this invention to adjust the -speed of the motor in such a way that the power output remains substantially constant, thereby ensuring a substantially constant tension upon the strip.

It has been found expedient to utilize a transmission mechanism having variable diameter pulleys, having a pair of sections that are relatively axially movable, provided with opposed inclined `faces cooperating with an edge-active belt. Then, by adjusting the relative axial positions of the pulley sections, the belt is caused to engage the sloping faces of the sections at adjusted radial distances from the axis of rotation. A variable ratio transmission mechanism of this character is described in Patent No. 2,398,235, issued April 9, 1946.

The motor driving the variable ratio transmission mechanism is arranged to be connected to a' source of electrical energy, the electromotive force of which isjcontrolled within narrow limits. Therefore, the value of the current consumed by the motor is a measure of its power, and

Patented Mar. 28, 1961 possible gradually to reduce or increase the tension on the strip as the winding progresses.

It is still another object of this invention to control the speed by the aid of penumatic devices. For example, the system is arranged to convert variations in the load current to variations in pneumatic pressure, to provide signal air. In turn, variations in the signal air are utilized to control the power air to be applied to la pneumatic pulley adjusting mechanism, which retains the adjustment once the signal air returns to the pressure corresponding to the desired value of load current.

It is still another object of this invention to ensure that when a new roll is connected to the drive for the beginning of a rewind operation, the transmission mechanism automatically assumes an output speed correspond ing to that required for a minimum roll diameter.

This invention possesses many other advantages, and has other objects which may be made more clearly apparent from a consideration of one embodiment of the invention. For this purpose, there is shown a form in the drawings accompanying and forming a part of the present specification. This form will now be described in detail, illustrating the general principles of the invention; but it is to be understood that this detailed description is not to be taken in a limiting sense, since the scope of this invention is best dened by the appended claims.

Referring to the drawings:

The single ligure is a diagrammatic representation of a system embodying the invention.

A web or strip 1 is shown as being rewound upon a roll 2. This roll 2 is indicated as driven by the aid of an output yshaft 3 and a clutch 3a connected to a device providing a source of motion 4. This device includes an induction motorl 4a, and an adjustable ratio transmission mechanism having variable diameter pulley structuresv 6. The device 4 is similar to that described and claimed in Patent No. 2,398,235, issued April 9, 1946, and particularly Figure 8 thereof.

Representative of the strip or web, the element l may be a fabric web or thin metal, suchfas aluminum. Obviously, it is essential to keep the tension constant or substantially constant as it is ybeing wound upon the roll 2 in a counterclockwise direction, for otherwiseeither the wound reel or roll is not lirm enough, or contrarywise an undesirable permanent elongation of the strip may result.

In order to effect this result, the power output of the device 4 is maintained substantially constant; i.e. rthe product of the torque imposed on winding roll 2, and the angular velocity must be substantially constant. This condition is fulfilled when'the current flow to motor 4a is kept within narrow limits. These limits can be manu-A ally set, as hereinafter described.

The variable transmission mechanism 6 has a ratio which can be continuously adjusted through a range as by the aid of a longitudinally adjustable stem 5. In the present instance, this adjustment is such that, as the wound up material on roll 2 increases in diameter, the speed of the driving shaft 3 is correspondingly reduced. As hereinabove mentioned, such a control serves to pro-V vide a substantially constant tension upon the material 1.

Although other means could be used, there is disclosed a pneumatic actuator 7 for urging the element S in a direction to decreasethe speed; that is, to move the pulley sections of the transmission mechanism further apart so as to reduce the effective diameter of the upper variable diameter pulley of the mechanism 6. Such a pneumatic actuator 7 is described in Patent No. 2,653,578, issued September 29, 1953, in the name of C.' B. Moore, as well as in various manufacturers bulletins, eg. Series 50 Cylinder Conomotors, a Bulletin No. BSO-2 of the Conoow Corporation, Philadelphia 3, Pennsylvania,

and bearing a printing date of January 1, 1955. This pneumatic actuator 7 responds to the pressure exerted by signal air `conducted by conduit 10 to this pneumatic actuator. The position of the actuator 7, and hence the speed of the shaft 3 are directly proportional to signal air pressure. This signal air pressure continues to cause operation of actuator 7 until the current consumed by motor 4a reaches the desired value.

The power required to move the member 5 is derived from a relatively high pressure conduit 8 that is connected through a' combined filter, regulator and gauge 9 to a commercial source of air. For example, the output or this regulator 9 (shown in the upper left-hand corner of the figure) may be of the order of twenty-tive pounds per square inch.

The pressure of the signal air in conduit 10 is varied in such a manner as to maintain the currentl consumed by device 4 at a `constant value. Such a result is etected by instrumentalities now to be described.

The motor 4a is fed from mains 11. In one of 'these mains is located `a current transformer 12, the secondary Winding of which is connected across a shunt resistance 13. The electromotive torce across the shunt resistance is impressed upon a rectifier 14, which may be adjusted to produce the desired output direct current.` The output of the rectier 14 is in direct proportion to the current in one of the mains 11, `and is preferably in the operative range of from zero to five milliamperes. This signal current has a normal value corresponding to the desired power consumption of the system. The current is caused to provide signal air pressures in conduit 10, as now to be described.

The direct current derived from the rectier 14 is fed to an electropneumatic transducer 15. This includes a valve mechanism delivering air at a pressure directly proportional to the current being fed to it. Air at a predetermined pressure is fed to the transducer 15 as by the aid of a conduit 16. This conduit is connected to the output side of the regulator 9 and passes through a combination lter, regulator and gauge 17 to reduce the input pressure to the transducer to `a definite value; for example, to eighteen pounds per square inch.

The output of the electropneumatic transducer is connected to an inverse derivative relay 18. This relay has `a power input from conduit 19 connected to the output of the regulator 9. This relay 18 serves to smooth out any violent or sudden variation in the output signal pressure from transducer 15. This is accomplished by causing the changes in pressure to occur over a period suiiicient to reduce the rate of change of pressure. Such devices are shown in Patents No. 2,431,297, issued November 18, 1947, and No. 2,501,957, issued March 28, 1950, to C. B. Moore.

The output conduit 20 of relay 18 is connected to the input side of a controller 21 having a power conduit 27 supplied from the output side of the regulator 9.

Relay 13 also supplies, via conduit 20, air pressure to the input of a manual control station 24. This station is manually `adjustable to provide -a desired set point or value of the normal signal current. This set point is led to the controller 21 by conduit 23. A comparison between the set point and the actual pressure in conduit 20 is made by controller 21, and an output pressure is transmitted via conduit 22. The output conduit 22 of the controller 21 impresses output pressure to the actuator 7. Controllers of the type represented by device 21 are described in Patents Nos. 2,312,201; 2,359,236; 2,518,244; and 2,520,468. See also pages 2 and 3 of Bulletin 5013 of Moore 'Products Co. of Philadelphia, Pennsylvania, entitled Nullmatic lVl/P Controller and Control Stations, copyrighted in 1957. Reference may also be made to instruction Book SD50-2A2 distributed by the same company and copyrighted in 1955.

Such controllers, as exemplified by Patent No. 2,312,-L

201, include a Valve having a closure that is disposed over the valve port. The closure is in the storm of a plate. The position of the plate is affected by air pressures exerted upon separate independent areas of the plate such as by the -aid of metallic bellows. The re- -sultant integrated air pressures aiect the position of the plate, and affect the signal pressure transmitted from the output. In this way, comparison between air pressures can be effected.

The manual control station 24 is provided with actuating air from conduit 27. The function of this station is described in Bulletin 5013, page 8 et seq. and hereinabove identified. See also Instruction Book SD-5231 and speciiically page 8, Fig. 1A. This bulletin was copyrighted in 1954 by Moore Products Co. The output conduit 25 of the station 24 leads to a high limit relay 26. This high limit relay is actuated by the pressure of power air in conduit 27 connected to the output side of the regulator 9. High limit relay 26 ensures that the maximum speed of motor 4a is limited to a value corresponding to the desired starting value.

The station 24 also provides an overriding ymanual control, independent of controller 21. Thus, this 'station may optionally by-pass the controller 21, and pass, air from the manual control station 24 directly to outlet conduit 25, whenever it is desired to do so.

Output conduit 25a of relay 26 is connected to the signal air conduit 10, via a manually adjustable needle valve`27a and a capacity chamber 28. This arrangement, including valve 27a and capacity chamber 28 serves to` reduce the fluctuations in the signal air conduit 10. lt is essential for smooth operation of the system.

As described above, the function of the controller 21 is to compare the air signal resulting from the current consumed by the motor 4a to the desired value of air signal introduced as a Set-Point from manual control station 24, via conduit 23. This set-point signal presf sure corresponds to the value of motor current which it is desired to maintain. The controller 21 will, by means of air pressure supplied to the pneumatic actuator 7, change the speed of the variable speed device 4 to whatever value is required in order to maintain coincidence of the signal pressure in conduit 20 (actual motor current) to set-poin pressure in conduit 23, corresponding to the desired motor current.

In order to provide for less tension in the web or strip at the end of winding than at the beginning, the set-point pressure in conduit 23 corresponding to desired motor current, must be continually reduced as the Winding progresses. relay 30.

This relay has an input conduit 32 derived from the output of controller 21. Another input conduit 31 is used, providing a bias pressure from the conduit 16, through a regulator 33. This regulator serves to provide a iixed pressure for the inlet 31. The output pressure in conduit 29 (which pressure is fed to the manual control station 24) can be made to be directly proportional to the dilerence in the pressures existing in conduits 31 and 32. By adjusting the areas of the openings from conduits 31 and 32 into a common conduit leading to output 29, this ratio can be chosen, as desired.

As the winding progresses, the input pressure in conduit 23 decreases proportionately with the speed drop which the controller 21 calls for in order to maintain the pressure in conduit 20 equal to that in conduit 23. Due to the operation of relay 30, the pressure in conduit 32 is attenuated by a ratio corresponding to the setting of relay 30. The amount of adjustment of the set point which takes place with a reduction in speed as the winding progresses is determined by this adjustment. This arrangement, by proper adjustment of the ratio relay 30, permits tapering the tension of the rewound strip or web 1 to be tighter wound at the start than at the iinish. A ratio relay of the type described herein is described,

This action is accomplished by ratio for example, in Bulletin 5430 of Moore Products Co. of Philadelphia, Pennsylvania, copyright 1954.

At the conclusion of the winding operation, the clutch 3a is disengaged, to permit removal of the Wound material. Such disengagement reduces the torque requirement of motor 4a to a minimum, and the controls just described would then operate to increase the speed of shaft 3. However, this speed is limited by the high limit relay 26. But in order to reset the mechanism or device 4 to a proper starting position, ay conduit 34 is connected between the output side of relay 26 and controller 21, which precisely causes the controlled speed to increase only to a proper starting value for the rewind operation.

The connection 314 is usually termed a feedback connection and is described in the publication hereinabove identified.

The inventor claims:

1. In combination: an electric motor; an adjustable ratio transmission mechanism driven by the motor, and adapted to operate a load; means for adjusting said mechanism as a function of applied pressure; means applying pressure to said adjusting means; and fluid pressure comparison means responsive to a deviation of the load current of the motor from a desired value for correspondingly changing the pressure applied to said adjusting means.

2. The combination as set forth in claim l, with the addition of a current transformer having a secondary winding, and a shunt resistor for the Winding, said shunt resistor supplying a low voltage signal; and means for converting said low voltage signal into a uid pressure signal for comparison by said uid pressure comparison means.

3. In combination: an electric motor; a transmission mechanism having a ratio continuously adjustable through a range to provide a variable output speed, and driven by said motor; a load driven by the mechanism and having an increasing torque requirement; fluid pressure means for determining the ratio of transmission as a function of signal pressure; means providing a signal pressure for the uid pressure means; means operating in response to deviations of the load current of the motor from a desired value, for correspondingly changing the signal pressure in a direction to reduce the deviations; and means for gradually changing the desired value with which the load current is compared.

4. In combination: an electric motor; a transmission mechanism having a ratio continuously adjustable through a range, and driven by said motor; a load driven by the mechanism and having an increasing torque requirement; uid pressure means for adjusting the mechanism; pneumatic means operating in response to deviations of the load current of the motor from a desired value, for causing the uid pressure means to adjust said mechanism substantially to nullify the deviation; and

means effective to reduce that value of the load current which controls the pneumatic means, comprising a ratio control station having both a signal air and fixed air in-V the mechanism; a load drivenv by the mechanism and having an increasing torque requirement; means for gradually kreducing the speed of the output of the transmission mechanism as operation of the transmission progresses; and means responsiveto disconnection of the load from the mechanism, for increasing the speed of the transmission output to a value corresponding to the desired speed of the load at the beginning of an operation.

6. The combination as set forth in claim 5, in which the adjusting means is signal air, the pressure of which is a measure of the current supplied to the motor, and with the addition of means for imposing a limit to the pressure of the signal air whereby a high speed adjustment is achieved.

7. In combination: an electric motor; an adjustable ratio transmission mechanism driven by the motor; a rewind roll driven by the mechanism; means responsive to deviations in current consumed by the motor to adjust the ratio of transmission, for correcting said deviations; and means for automatically reducing the value of the current that controls the adjusting means, in accordance with increase in the size of the roll.

8. The combination as set forth in claim 1 together with a transducer for converting load current values into a uid pressure signal for comparison by said uid pressure comparison means.

y9. The combination as set forth in claim 1 together with means for changing the desired value with which the load current is compared and as a function of said applied pressure.

10. The combination as set forth in claim 1 together with means for changing the desired value with which the load current is compared; and selectively adjustable means for operating said changing means as a function of said applied pressure.

11. The combination as set forth in claim 1 in which said load has a continuously increasing torque requirement together with means for limiting the signal air to a predetermined value in order to determine the starting speed when the load is removed.

References Cited in the ile of this patent UNITED STATES PATENTS 2,348,090 Otto May 2, 1944 2,350,913 Mercer June 6, 1944 2,581,328 Malcolm Ian. 1, 1952 2,796,222 Frankel June 18, 1957 

